title: The quantitative surface analysis of an antioxidant additive in a lubricant oil matrix by desorption electrospray ionization mass spectrometry.
abstract: BACKGROUND
  Chemical additives are incorporated into commercial lubricant oils to modify the physical and chemical properties of the lubricant. The quantitative analysis of additives in oil-based lubricants deposited on a surface without extraction of the sample from the surface presents a challenge. The potential of desorption electrospray ionization mass spectrometry (DESI-MS) for the quantitative surface analysis of an oil additive in a complex oil lubricant matrix without sample extraction has been evaluated.
  
  
  METHODS
  The quantitative surface analysis of the antioxidant additive octyl (4-hydroxy-3,5-di-tert-butylphenyl)propionate in an oil lubricant matrix was carried out by DESI-MS in the presence of 2-(pentyloxy)ethyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate as an internal standard. A quadrupole/time-of-flight mass spectrometer fitted with an in-house modified ion source enabling non-proximal DESI-MS was used for the analyses.
  
  
  RESULTS
  An eight-point calibration curve ranging from 1 to 80 µg/spot of octyl (4-hydroxy-3,5-di-tert-butylphenyl)propionate in an oil lubricant matrix and in the presence of the internal standard was used to determine the quantitative response of the DESI-MS method. The sensitivity and repeatability of the technique were assessed by conducting replicate analyses at each concentration. The limit of detection was determined to be 11 ng/mm(2) additive on spot with relative standard deviations in the range 3-14%.
  
  
  CONCLUSIONS
  The application of DESI-MS to the direct, quantitative surface analysis of a commercial lubricant additive in a native oil lubricant matrix is demonstrated.
authors.affiliation: Centre for Analytical Science, Department of Chemistry, Loughborough University, Loughborough, LE11 3TU, UK.
authors.forename: Caitlyn
authors.initials: C
authors.lastname: Da Costa
authors.forename: James C
authors.initials: JC
authors.lastname: Reynolds
authors.forename: Samuel
authors.initials: S
authors.lastname: Whitmarsh
authors.forename: Tom
authors.initials: T
authors.lastname: Lynch
authors.forename: Colin S
authors.initials: CS
authors.lastname: Creaser
mesh_terms: D000975:Antioxidants / Q000032:analysis*; D002073:Butanes / Q000032:analysis*; D057230:Limit of Detection; D054327:Lubricants / Q000737:chemistry*; D011422:Propionates / Q000032:analysis*; D015203:Reproducibility of Results; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: C513029:3,5-di-tert-butyl-4-hydroxyphenyl; D000975:Antioxidants; D002073:Butanes; D054327:Lubricants; D011422:Propionates